Desilverizing lead bullion.



UNITED STATES PATENT OFFICE.

AUGUST RAHT, OF SAN FRANCISCO, CALIFORNIA.

DESILVERIZING LEAD BULLION.

Specification of Letters Patent.

Patented July 17, 1906.

Application filed October 11, 1905. Serial No. 282,277.

To all whom, it may concern;

Be it known that I, AUeUsT RAHT, a citizen of the United States, residin at San Francisco, in the county of San Francisco and State of California, have invented certain new and useful Improvements in Proc esses of Desilverizing Lead Bullion, of which the following is a specification.

This invention relates to the treatment of lead bullionthat is, an ar'gentiferous or auriferous alloy of lead; and its object is to render a more speedy and effectual separation of the lead from the precious metals.

After the bullion has been freed of its copper, antimony, and arsenic in a softening furnace metallic zinc is added and stirred therein, as customary, to cause the contained gold and silver, for which it has an affinity, to rise to the surface in the form of a scum containing more orlesslead, according to the character of the alloy and the manner of carrying out the rocess. This scum or zinc skin is skimme off from the liquid lead by means of perforated ladles and undergoes further treatment by retorting off the zinc and cupeling to eliminate the lead, and thus obtain the silver and gold.

According to my invention a small quantity of sal-ammoniac or chlorid of ammonium, as it is usually termed, or another similar salt is added shortly after the zinc has been introduced and thoroughly stirred with the molten metals and'effects the more complete separation of the lead from the scum than is possible by the mechanical means alone above referred to. This supplementary step in the smelting process not only thus reduces the bulk of scum to be operated upon, but likewise causes it to be in a drier state'i. e. ,containing less lead, and conseuently more easily and cheaply treated in t e following refining processes.

While my invention is a supplemental step to the various aforementioned customary ones, the additional cost is so slight as to be insignificantwhen the resulting economy in the retorting and cupelation is considered. The amount of the ammoniacal salt for a given quantity of the metal will vary according to the requirements in each particular case; but ordinarily one ound of the same will suffice for ten tons of ullion.

Having thus explained my invention, what I claim as new, and desire to secure byLetters Patent, is

1. The treating of lead bullion while in a molten state consisting in adding zinc thereto and then adding sal-ammoniac for the purpose of causing a more ready and complete separation of the lead therefrom.

2. The process of treating lead bullion consisting in adding Zinc to a molten mass thereof, then adding sal-ammoniac, then stirring the mixture so as to separate from the scum which is formed by the addition of the zinc a portion of the lead contained in the scum.

3. The herein-described improvement in the rocess of desilverizing lead bullion, whicl i consists in heating an argentiferous alloy of lead to melt the same, then adding metallic zinc to cause the separation of a. portion of the lead from the more precious metals, and then adding sal-ammoniac to suchincompletely-separated mass to effect a further elimination of the remaining lead therefrom.

In testimony whereof I afiiX my signature in presence of two witnesses.

AUGUST RAHT.

Witnesses:

PIERRE BARNES, C. F. WHITTLEsEY. 

